Response to “Correlating blood mercury and dental amalgams” by Claudio Minoia and co-workers

Abstract

To the Editor: Minoia and co-workers claimed that methodological details about the calculation of the number of amalgam fillings among participants were missing in our recent study on mercury exposure in Austria (Gundacker et al., 2006). This issue can be simply defused: the number of amalgam fillings was self-reported by study participants and was not determined by a dentist. We agree that precise calculation of the amalgam filling surfaces by a trained dentist might have increased the strength of correlation between the number of fillings and blood mercury contents. We have not surveyed gum chewing habits; this variable should be included in future studies on mercury exposure through amalgam fillings in the Austrian population. The same applies to other potential confounders associated with mercury release from dental fillings. According to Eley (1997), gum chewing, mixed food chewing, and tooth brushing are the three stimulating factors for mercury release from amalgam surfaces. Our study was not designed to primarily investigate the relationship between amalgam fillings and mercury exposure, which would have required either the inclusion of more individuals or an a priori different study design. In such a study, fish eaters would have to be excluded (93% of our study participants were fisheaters) and the questionnaire would need to provide detailed information on gum chewing habits (type of chewing gum, frequency of gum chewing), eating habits (number and duration of meals, type of meal, particularly mixed food chewing) and tooth brushing habits (frequency and duration of tooth brushing, type of tooth brush, type of tooth paste). One study result was that women – in contrast to the entire group and to the male subgroup – did not indicate mercury exposure through amalgam fillings. Although the strength of the correlation (amalgam fillings/blood mercury) may well have increased with a more precise calculation of filling number, we do not think that it would have fundamentally altered this finding, i.e. women reflected mercury exposure through amalgam fillings with less statistical significance than men. Finally, we would have had to measure mercury species to prove the observed relationships between dental amalgam and blood mercury loads of women and men. These many interesting aspects clearly go beyond the scope of the present study, but deserve examination in future investigations. References